1. Field of the Invention
The present invention relates to an internally threaded fastener having a smooth forward end portion and which provides for maximum retaining ring retention.
2. Description of the Prior Art
Prior art internally threaded fasteners that have a smooth, probing lead-in feature suffer in that the panel retaining device utilized to secure the fastener to the panel itself may slip off the fastener. The prior art internally threaded fasteners which typically comprise a stud having an internally threaded aperture, a grommet which functions to both retain the stud to the panel and maintain the stud in an upright, or hold-out, position when the stud is disengaged from a substructure, and a receptacle which contains a threaded screw for insertion into the stud aperture typically utilize a flexible wire type ring that expands and retracts depending on the diameter of the fastener portion it resides on at a given point of time as shown, for example, in U.S. Pat. No. 2,991,816 to Harbison et al. In particular, this type of ring causes retention problems because it has to accommodate three different diameters to function properly. As a result, its holding capabilities are limited. This problem is aggravated when angularity, twisting and pull-out of the fastener is attempted, often resulting in the conventional retaining ring slipping off the fastener.
These types of fasteners are typically utilized to fasten doors to an airplane frame, the grommet typically fitting into the frame (substructure) when the fastener is assembled. However, side loads created by the fuel and/or other loading added to the airplane can make it extremely difficult for the grommet to be removed from the substructure aperture thus preventing the door from being opened.
U.S. Pat. No. 4,324,517 to Dey discloses a panel fastener assembly which seeks to overcome the disadvantages of the Harbison et al. fastener, i.e. the spring has not reliably and consistently retained the sleeve bolt in the panel when the panel is disengaged from the aircraft substructure. The Dey assembly includes a sleeve bolt, a grommet assembly which is attached to the panel and a receptacle assembly which is attached to the substructure. The sleeve bolt passes through the grommet assembly and engages the receptacle assembly thereby joining the panel and the substructure. The grommet assembly includes a retainer ring which engages a groove in the sleeve bolt when it is in its withdrawn position so that the sleeve bolt is retained in the panel and remains in its withdrawn position when the panel is disengaged from the substructure.
Although the Dey device improves over the earlier Harbison et al. fastener, it still have disadvantages. For example, the single retainer ring utilized must repeatedly pass through at least two diameters during its use and thus could be subject to failure. Further, side loads on the sleeve bolt in the substructure may make it difficult to remove the sleeve bolt. The Dey device, although improving the retaining ring holding capability, sacrifices the probing or misalignment feature of the Harbison fastener. This feature comprises an area below the grip portion of the Harbison fastener is reduced in diameter to aid in installation of the fastener by allowing the operator to search for the receptacle when the holes are misaligned. As the fastener is secured, the full diameter of the grip section aligns the outer panel perfectly with the substructure hole. It also aids the operator when the fastener is to be removed. As the fastener is unloosened, the outer panel is allowed some misalignment when the full diameter of the grip section exits the substructure. This occurs because the diameter of the fastener adjacent to the grip portion is significantly smaller. The Dey device does not incorporate this probing feature of Harbison.
What is thus desired is to provide an internally threaded fastener in which the panel retaining ring utilized is configured to have maximum retention capabilities, wherein a structural feature of the fastener is used to eject the grommet from the substructure as the stud is being disengaged from the receptacle screw and wherein the fastener has a reduced entrance diameter for maximum probing capability.